The present invention relates to a correlation function measuring method and apparatus, more specifically to a correlation function measuring method and apparatus for measuring a correlation vector of a plurality of input signals.
Recently, a technique for visualizing a wave source image by electric wave holography has been practiced and is used, e.g., in monitoring electric waves from base stations for portable telephones. Electric wave holograms of electric waves from base stations of a portable telephone network are analyzed to thereby visually monitor the electric waves from the base stations so as to obtain materials useful to judge whether or not to install a new base station.
A wave source image visualizing method and apparatus has been proposed by the applicant of the present application in, e.g., the specification of Japanese Patent Application No. 289848/1995.
The wave source image visualizing method and apparatus proposed by the applicant of the present application will be explained with reference to FIG. 8. FIG. 8 is a block diagram of the proposed wave source image visualizing apparatus.
As shown in FIG. 8, a monitored signal (a) received by a stationary antenna (not shown) is subjected to prescribed signal processing by the pre-conversion unit 218a, a data memory 220a and Fourier-transform unit 222a to be inputted to a correlation vector computing unit 230 while a monitored signal (b) received by a scanning antenna (not shown) is subjected to prescribed signal processing by a pre-conversion unit 218b, a data memory 220b and a Fourier-transform unit 222b to be inputted to the correlation vector computing unit 230. The pre-conversion units 218a, 218b restrict the monitored signal (a) and the monitored signal (b), based on a center frequency f0 and a band width bw to convert them to IF signals and output the IF signals. The data memories 220a, 220b perform an analog-to-digital (A/D) conversion process on the IF signals and store the A/D converted signals therein. The Fourier-transform units 222a, 222b perform Fourier-transformation to output a spectrum SA(f) and a spectrum SB(f).
In the correlation vector computing unit 230, based on the following formula,                               ∫                                    f              0                        -                          bw              2                                                          f              0                        +                          bw              2                                      ⁢                                                                              S                  A                  *                                ⁡                                  (                  f                  )                                            ·                                                S                  B                                ⁡                                  (                  f                  )                                                                    "LeftBracketingBar"                                                S                  A                                ⁡                                  (                  f                  )                                            "RightBracketingBar"                                ⁢                      ⅆ            f                                              (        1        )            
a correlation vector is given, where * represents a complex conjugate.
In such a wave source image visualizing apparatus, when measuring conditions, such as band width restriction, frequency conversion, etc., are changed, frequency characteristics of the pre-conversion units 218a, 218b change. Furthermore, the frequency characteristic change varies between the pre-conversion unit 218a and the pre-conversion unit 218b. 
Accordingly, it is necessary to prepare in advance correction data, and a correlation vector is corrected by using the correction data. The wave source image visualizing apparatus shown in FIG. 8 gives correction data xcfx81(c) in the following way.
That is, when correction data xcfx81(c) is given, switches 216a, 216b, 224 are set on a correction side (c), correction signals are outputted by a signal generator 212, the correction signals are distributed to two paths by the power splitter 214, the correction signals are inputted to the correction sides (c) of the switches 216a, 216b, and a correlation vector is given by the correlation vector computing unit 230. A value of the given correlation vector is stored in a correction data memory 228 as the correction data xcfx81(c).
For electric wave monitor, the switches 216a, 216b, 224 are set on a measuring side (m), and a correlation vector is given by the correlation vector computing unit 230. The given correlation vector is corrected in a correction unit 229 by using the correction data xcfx81(c) to be outputted to a wave source image reproduction processing unit (not shown).
The wave source image reproduction processing unit performs prescribed image processing, and a processed image is presented on a display of a display unit (not shown).
However, in the proposed wave source image visualizing apparatus, a correlation vector of an average of band frequencies given when a correction signal is inputted is used as correction data xcfx81(c). Accordingly, in a case that characteristics of the pre-conversion units 218a, 218b change by frequencies, correction accuracy varies depending on frequencies.
Characteristics of the pre-conversion units 218a, 218b are varied by changes of measuring conditions, surrounding temperature changes, changes over time, etc. The proposed wave source image visualizing apparatus has correction accuracy lowered by these factors.
An object of the present invention is to provide a correlation function measuring method and apparatus which can correct a correlation vector with high accuracy.
The above-described object is achieved by a correlation function measuring method in which a first monitored signal is processed by a first signal processing means to give a first spectrum, a second monitored signal is processed by a second signal processing means to give a second spectrum, and a correlation function between the first spectrum and the second spectrum is measured, the method comprising the steps of: inputting, before measuring the correlation function, correction signals to the first signal processing means and the second signal processing means, and giving correction values corresponding to frequencies of the correction signals, based on a spectrum given by the first signal processing means, and a spectrum given by the second signal processing means; and in measuring the correlation function, giving a correlation function between the first spectrum and the second spectrum by using the correction values corresponding to the frequencies. Correction data for respective frequencies are given before a correlation function is measured, and the correlation function is given by using the correction data corresponding to the frequencies, whereby the correlation function can be given with high accuracy. Thus, the correlation function measuring method can measure a correlation function with high accuracy.
In the above-described correlation function measuring method it is preferable that in giving the correction values, the frequencies of the correction signals are scanned to give the correction values corresponding to the respective frequencies.
In the above-described correlation function measuring method it is preferable that a recurrence formula is given based on the correction values; and in renewing the correction values, correction values necessary to determine at least the recurrence formula are again given to renew the recurrence formula, and based on the renewed recurrence formula, the correction values are renewed.
In the above-described correlation function measuring method it is preferable that in giving the correction values, modulated waves are inputted to the first signal processing means and the second signal processing means to give correction values corresponding to respective frequencies.
In the above-described correlation function measuring method it is preferable that in giving the correction values, first correction signals are inputted to the first signal processing means and the second signal processing means, scanning frequencies, to give magnitude correction data corresponding to the frequencies, based on a spectrum given by the first signal processing means and a spectrum given by the second signal processing means, and second correction signals are inputted to the first signal processing means and the second signal processing means to give phase correction data corresponding to the respective frequencies, based on a spectrum given by the first signal processing means and a spectrum given by the second signal processing means, and the correction values corresponding to the respective frequencies are given based on the magnitude correction data and the phase correction data. Magnitude correction data, which are not frequently necessary, are produced by using first correction signals, while phase correction data, which are frequently necessary, are produced by using second correction signals, and correction values corresponding to the respective frequencies are given by using the correction data, whereby the correction can be quickly made without lowering correction accuracy.
In the above-described correlation function measuring method it is preferable that the second correction signals are modulated waves.
In the above-described correlation function measuring method it is preferable that in giving the magnitude correction data, the frequencies of the first correction signals are scanned at a prescribed step and interpolated to give the magnitude correction data.
In the above-described correlation function measuring method it is preferable that the phase correction data are renewed more frequently than the magnitude correction data.
In the above-described correlation function measuring method it is preferable that when the renewed phase correction data are changed by an amount above a prescribed value with respect to the phase correction data at the time of obtaining the magnitude correction data, the magnitude correction data is renewed.
The above-described object is achieved by a correlation function measuring apparatus comprising: first signal processing means for processing a first monitored signal to give a first spectrum; second signal processing means for processing a second monitored signal to give a second spectrum; correction value computing means for inputting correction signals to the first signal processing means and the second signal processing means to give correction values corresponding to frequencies, based on the spectrum given by the first signal processing means and the spectrum given by the second signal processing means; correlation function computing means for giving a correlation function between the first spectrum and the second spectrum by using the correction values given by the correction value computing means. Correction data for respective frequencies are given before a correlation function is measured, and the correlation function is given by using the correction data corresponding to the frequencies, whereby the correlation function can be given with high accuracy. Thus, the correlation function measuring apparatus can measure a correlation function with high accuracy.
In the above-described correlation function measuring apparatus it is preferable that the correction value computing means gives the correction values corresponding to the frequencies by scanning the frequencies of the correction signals.
In the above-described correlation function measuring apparatus it is preferable that the correction value computing means gives a recurrence formula, based on the correction values, again giving correction values necessary to determine at least the recurrence formula to renew the recurrence formula, and renewing the correction values, based on the renewed recurrence formula.
In the above-described correlation function measuring apparatus it is preferable that the correction value computing means gives the correction values corresponding to the respective frequencies by inputting modulated waves to the first signal processing means and the second signal processing means.
In the above-described correlation function measuring apparatus it is preferable that the correction value computing means inputs first correction signals to the first signal processing means and the second signal processing means, scanning frequencies, gives magnitude correction data corresponding to the respective frequencies, based on the spectrum given by the first signal processing means and the spectrum given by the second signal processing means, inputting second correction signals to the first signal processing means and the second signal processing means to give phase correction data corresponding to the frequencies, based on the spectrum given by the first signal processing means and the spectrum given by the second signal processing means, and gives the correction values corresponding to the respective frequencies, based on the magnitude correction data and the phase correction data. Magnitude correction data, which are not frequently necessary, are produced by using first correction signals, phase correction data, which are frequently necessary, are produced by using second correction signals, and correction values corresponding to the respective frequencies are given by using the correction data, whereby the correction can be quickly made without lowering correction accuracy.
In the above-described correlation function measuring apparatus it is preferable that the second correction signals are modulated waves.
In the above-described correlation function measuring apparatus it is preferable that the correction value computing means scans the frequencies of the first correction signal at a prescribed step and interpolates to give the magnitude correction data.
In the above-described correlation function measuring apparatus it is preferable that the correction value computing means renews the phase correction data more frequently than the magnitude correction data.
In the above-described correlation function measuring apparatus it is preferable that the correction value computing means renews the magnitude correction data when the renewed phase correction data has changed by an amount above a prescribed value with respect to the phase correction data given at the time for obtaining the magnitude correction data.